T-Type Ca2+ channels (T-channels), particularly Cav3.2, are now considered as therapeutic targets for treatment of
intractable pain including
visceral pain. Among existing medicines,
bepridil, a multi-channel blocker, used for treatment of
arrhythmia and angina, and
pimozide, a
dopamine D2 receptor antagonist, known as a typical
antipsychotic, have potent T-channel blocking activity. We thus tested whether
bepridil and
pimozide could suppress
visceral pain in mice. Colonic and bladder
pain were induced by intracolonic administration of
2,4,6-trinitrobenzene sulfonic acid (TNBS) and systemic administration of
cyclophosphamide (CPA), respectively. Referred
hyperalgesia was assessed by von Frey test, and colonic
hypersensitivity to distension by a volume load with intracolonic water injection and spontaneous bladder
pain were evaluated by observing nociceptive behaviors in conscious mice. The mice exhibited referred
hyperalgesia and colonic
hypersensitivity to distension on day 6 after TNBS treatment. Systemic administration of
bepridil at 10-20 mg/kg or
pimozide at 0.1-0.5 mg/kg strongly reduced the referred
hyperalgesia on the TNBS-induced referred
hyperalgesia and colonic
hypersensitivity to distension. CPA treatment caused bladder
pain-like nociceptive behavior and referred
hyperalgesia, which were reversed by
bepridil at 10-20 mg/kg or
pimozide at 0.5-1 mg/kg. Our data thus suggest that
bepridil and
pimozide, existing medicines capable of blocking T-channels, are useful for treatment of colonic and bladder
pain, and serve as seeds for the development of new medicines for
visceral pain treatment.